Performance for CMP in Concurent Requersts

whenever we will sent to multiple Requests threw servlet that requests process sequentially, here we are observing all requests reached up to stateless session bean executing concurently whenever we are called any entity bean in side session bean that time onwards second request waiting mode up to first request processing completed after only second request process starts .....(this process will going on all multiple Requests). why this situation happend i am not understading please help me.